1. Field of the Invention
The present invention relates to an organic light emitting element.
2. Description of the Related Art
An organic light emitting element is an element including an anode, a cathode, and an organic compound layer arranged between the electrodes. A hole and an electron to be injected from the electrodes recombine in a light emitting layer in the organic compound layer to produce an exciton, and the organic light emitting element emits light upon return of the exciton to its ground state. Recent development of the organic light emitting element is significant, and allows the organic light emitting element to be a light emitting device having the following features: a low driving voltage; light emission at various wavelengths; high-speed responsiveness; a small thickness; and a light weight.
In the organic light emitting element, it is important to improve charge injecting property for reducing a voltage of the element. In order to improve the electron injecting property, an inorganic material such as lithium fluoride is generally used, but lithium fluoride is not a suitable material from the viewpoint of a lifetime of the element owing to its hygroscopicity.
As a method of improving electron transport property, there is given, for example, a method involving using a metal salt such as a compound 1-A disclosed in International Publication No. WO2013/079676.

In addition, in Inorganic Chemistry (1985), 24(10), 1454-7, there is a disclosure of a synthesis example of a compound using potassium, and in Journal of the American Chemical Society (1967), 89(24), 6288-94, there is a disclosure of a synthesis example of a compound using sodium.
As described above, the metal salt such as lithium fluoride to be generally used as an electron injecting material is water-soluble. Use of such compound in a layer of the organic light emitting element causes a reduction in stability of the light emitting element. Also the compound 1-A disclosed in International Publication No. WO2013/079676 is also a water-soluble material, and hence causes a reduction in stability of the light emitting element. In addition, in International Publication No. WO2013/079676, there is only a disclosure of a synthesis example of a metal complex in which three or more pyrazole groups are coordinated, such as the compound 1-A. Further, in International Publication No. WO2013/079676, the compound 1-A is used in an electron transport layer, which is not brought into contact with an electrode of a light emitting element, not in an electron injecting layer, which is brought into contact with the electrode. In addition, the metal complex such as the compound 1-A has low electron transport property, and hence provides an element requiring a high voltage when used alone in a transport layer having a thickness of several tens of nanometers.
In addition, in Inorganic Chemistry (1985), 24(10), 1454-7 and Journal of the American Chemical Society (1967), 89(24), 6288-94, there are not disclosures of any synthesis example of a compound using lithium and use of the compound using potassium and the compound using sodium in the organic light emitting element.